1. Field of the Invention
This invention relates to a printer device for emitting a printer device for mixing a medium for quantitation and a medium for emission and emitting the resulting mixed mediums. More particularly, it relates to a printer device in which the pressure applied to at least one of the medium for quantitation and the medium for emission for enabling correct gradation representation.
2. Description of the Related Art
Recently, computerized document preparation, termed desk publishing, has become popular particularly in an office, such that an increasing demand is raised for outputting not only letters or figures but also colored natural images, such as photos, along with the letters or figures. In keeping up therewith, it is required to have a natural image printed to a high quality such that gradation representation by regeneration of a half tone is becoming crucial. On the other hand, a so-called on-demand type printer device, which emits ink droplets only when required for effecting printing on a recording material, such as paper sheets or films, responsive to printing signals, is being used in increasing numbers because it can be reduced in size and cost.
Among a variety of methods for emitting the ink droplets, a method employing a piezoelectric device and a device employing a heat emitting device are most popular. The former method applies a pressure to the ink by deformation of the piezoelectric device for emitting the ink, while the latter method heats and vaporizes the ink by the heating device for generating bubbles for pressurizing and emitting the ink.
There are a variety of methods proposed for virtually realizing the above-mentioned gradation representation by manifesting the half-tone with the above-mentioned on-demand type printer device emitting the ink liquid droplets. The first of these varies the voltage or pulse width of voltage pulses applied to the piezoelectric device or the heating device for controlling the size of the emitted liquid drop to vary the diameter of the printing dots for representing the gradation.
However, with this method, the ink becomes unable to be emitted if the voltage or the pulse width applied to the piezoelectric device or the heating device is lowered excessively. Thus, there is a limitation to the minimum liquid drop size such that the number of stages of the gradation that can be represented is only small. In particular, the low concentration cannot be represented with ease such that the natural image cannot be printed out satisfactorily.
The second method is to construct a pixel of an image by a matrix of, for example, 4.times.4 dots, without varying the dot diameter, and to represent the gradation by picture processing such as the so-called dither method or the error diffusion method on the matrix basis.
With this second method, 17 stages of the concentration can be represented if each pixel is constructed by 1 4.times.4 matrix. However, if this second method is used for printing with the same dot density as that in the first method, the resolution is one-fourth of that of the first method such that an extremely coarse image is produced. Thus, this second method is insufficient for printing out the natural image.
For overcoming the problems of the conventional on-demand printer device as a principle, the present inventors have proposed a printer device in which the ink and a dilution liquid as a transparent solvent are mixed at a pre-set mixing ratio directly before emission to give a diluted ink which is then immediately emitted at a nozzle for deposition on a recording support to effect printing, as disclosed in, for example, the Japanese Laying-Open Patent H-5-201024 and H-7-195682. The system of this type in which the ink is the quantitation medium and the dilution liquid is the emission medium, the ink as the quantitation medium is mixed with the dilution liquid as the emission medium to give a diluted ink and the emission medium is emitted to effect recording, is termed a `carrier jet` system. In the above printer device, no problem is raised if the dilution liquid is the quantitation medium and the ink is the emission medium.
In such `carrier jet` printer device, the quantity of the quantitation medium, which is the ink or the dilution liquid, can be varied to vary the mixing ratio between the ink and the dilution liquid to control the concentration of the emitted mixed solution to vary the concentration from one printed dot to another. Thus it becomes possible to print out a natural image replete with the half tone gradation without deterioration in resolution.
The above-described two liquid mixing type printer device may, for example, be a so-called inner mixing type printer device. This inner mixing type printer device at least has an emission medium pressurizing chamber charged with the emission medium, an emission medium nozzle communicating with the emission medium pressurizing chamber, a quantitation medium pressurizing chamber into which is introduced the quantitation medium, and a connecting portion for connecting the quantitation medium pressurizing chamber to the emission medium nozzle. The quantitation medium in the quantitation medium pressurizing chamber is mixed with the emission medium in the emission medium nozzle via the connecting portion and the quantitation medium is mixed with the emission medium in the emission medium nozzle to form a mixed solution which is emitted at the emission medium nozzle.
However, in the above-described inner mixing type printer device, the quantitation medium tends to be diffused into the emission medium in the emission medium nozzle during the operation stand-by time when the quantitation medium is not mixed with the emission medium. In addition, the emission medium is likely to flow unnecessarily into the connecting portion during mixing-emission of the quantitation medium and the emission medium, or the quantitation medium is likely to flow unnecessarily into the emission medium.
If such diffusion between the quantitation medium and the emission medium occurs, the dilution liquid as the emission medium is gradually colored, or the quantitation medium, such as the ink, is diluted, thus affecting the concentration of the emitted mixed liquid droplets to render it difficult to obtain the correct gradation in concentration.
The above-mentioned unnecessary inflow is produced by the fact that, if a mixed solution of the ink as the quantitation medium and the dilution liquid as the emission medium, having an extremely thin concentration, is emitted continuously, the dilution liquid is intruded under pressure gradually into the ink-supplying connecting portion, or that, if the above mixed solution having a thick concentration is emitted continuously, the ink is intruded under pressure gradually into the emission medium nozzle. In case of unnecessary inflow in the former case, the mixed liquid droplets of a thin concentration are emitted when next the mixed solution of the thick concentration is desired to be emitted, whereas, in case of unnecessary inflow in the former case, the mixed liquid droplets of a thick concentration are emitted when next the mixed solution of the thin concentration is desired to be emitted, to render it difficult to realize correct concentration gradation.
Thus, in a conventional printer device, a unidirectional valve, prepared by, for example, electro-casting, is provided in a boundary between the connecting portion supplying the quantitation medium and the emission medium nozzle to prevent diffusion of the quantitation medium and the emission medium during the emission stand-by time as well as to prevent inflow between the two mediums during the mixing emission operation.
However, it is not that easy with the above-mentioned unidirectional valve to realize complete isolation between the two mediums during the emission stand-by time or complete prevention of the inflow between the two mediums during the mixing emission operation to render it difficult to realize correct concentration gradation. Moreover, such unidirectional valve leads inevitably to increased production cost to lower the productivity.
In order to evade such inconvenience, a so-called external mixing type printer device has also been proposed. This printer device has a quantitation medium pressurizing chamber into which a quantitation medium is introduced and an emission medium pressurizing chamber into which an emission medium is introduced, with a quantitation medium nozzle communicating with the quantitation medium pressurizing chamber and an emission medium nozzle communicating with the emission medium pressurizing chamber being opened in adjacency to each other. The quantitation medium is extruded towards the emission medium nozzle from the quantitation medium nozzle along the nozzle opening surface and brought into contact with the emission medium charged in the vicinity of the distal end of the emission medium nozzle to form a mixed solution. The emission medium then is emitted via the emission medium nozzle for externally mixing the quantitation medium and the emission medium to emit the resulting mixed solution at an outside.
Since the quantitation medium nozzle is formed separately from the emission medium nozzle, there is no risk of diffusion of the quantitation medium and the emission medium during emission stand-by time or inflow of the two mediums during the mixing and emission operation.
In the above-described printer device for mixing the ink as the quantitation medium and the dilution liquid as the emission medium and for emitting the resulting mixture, the mixing ratio between the ink and the dilution liquid needs to be controlled correctly for correct representation of the gradation corresponding to image data. In the above-described external mixing type printer device, the ink and the dilution liquid can be separated from each other in the state in which the ink and the dilution liquid are not as yet mixed together, that is in the emission stand-by state.
However, in this external mixing type printer device, there are occasionally presented problems that, when the liquid surface of the emission medium reverts to the opening end of the emission medium nozzle after mixing and emission, the emission medium overflows the emission medium nozzle to flow into the quantitation medium nozzle, or the liquid surface of the quantitation medium after mixing and emission overflows the quantitation medium nozzle due to reaction to the quantitation operation to flow into the emission medium nozzle.
In case of such relative inflow of the ink and the dilution liquid, the mixing ratio between the ink and the dilution liquid for the next dot is affected to render it impossible to represent the gradation correctly to render generation of the high-quality recording image difficult.